Reactivity of thiophenoxide ion toward o- and p-halogenonitrobenzenes

Abstract

Kinetic data for the thiophenoxy-dehalogenation of o- and p-fluoro- and -bromo-nitrobenzene in methyl and t-butyl alcohols in the absence or presence of dicyclohexyl-18-crown-6 at 50° are reported. In methyl alcohol the ortho : para ratios were found to be 1·46 (fluoro-substrates) and 0·32 (bromo-substrates) in the absence of crown ether, and 1·37 (fluoro-substrates) and 0·32 (bromo-substrates) in the presence of crown ether. In t-butyl alcohol the ortho : para ratios were found to be 28·1(fluoro-substrates) and 5·33 (bromo-substrates) in the absence of crown ether, and 1·44 (fluoro-substrates) and 0·43 (bromo-substrates) in the presence of crown ether. The rates of reaction of fluoro- and bromo-substrates in methanol with lithium thiophenoxide were also measured but no change in reactivity with respect to potassium thiophenoxide was detected in this solvent. The reasons for the increase in the ortho : para ratio on going from methyl to t-butyl alcohol as solvent are discussed.